Tubular elements such as casing and completion tubing, screens and other such devices are well known in the field of oil and gas wells. In order for tubular elements to be installed in the well, it is necessary that the tubular elements have an outer diameter that is less than the inner diameter of the borehole in which they are to be installed. In fact, since the inner diameter of the borehole can vary and the trajectory of the borehole is often not straight, the maximum possible diameter can be significantly less than that of the borehole at any point.
When a borehole is being drilled, it is usually necessary to stop drilling after a certain depth and stabilize the borehole by placing a steel tubular casing in the well and filling the annulus between the outside of the casing and the borehole wall with cement. This operation may need to be repeated several times during the drilling of the well, each successive casing being necessarily smaller than the inside diameter of the preceding casing. This in turn leads to progressive reduction of the inner open diameter of the well which in turn places limitations on the maximum depth of the well and on the quantities of fluids that can flow along the well.
To overcome this problem, it has been previously proposed to expand the casing in the well to reduce the annular space. Also, expansion of subsequent casings to match the diameter of the previous casing has also been proposed to avoid the progressive diameter reduction found with conventional casing techniques.
Expansion is typically achieved using a cone shaped expanding tool having a maximum diameter that is greater than the inside diameter of the casing to be expanded. Forcing the expanding tool through the casing (for example by mechanically pushing or pulling or by pumping a fluid) causes the casing to expand. One difficulty in this operation is that because the outer diameter of the expansion tool is greater than the inner diameter of the casing, it is not possible to position the expanding tool in the casing; it must either start at the top or bottom and be moved either to the other end or back to its starting place to be removed from the casing (or left in the well). To address this, expanding tools/cones have been proposed that are initially positioned in a contracted state and then are reconfigured into their (larger) operational configuration before being moved through the casing. However, since the outer diameter is still greater than the inner diameter of the casing, this must be done in an open section of the well or in a section of wider diameter. A recent alternative proposal is for the tool to apply enough force during deployment to expand the casing.